1. Field of the Disclosure
Embodiments disclosed herein relate generally to catalytic alkylation and transalkylation of benzene using a C2-C4 olefin and a heterogeneous catalyst slurry, which can be continuously replaced during operation.
2. Background
Alkylation refers generally to a type of chemical reaction resulting in addition of an alkyl group to an organic compound. Olefins, such as ethylene, propylene, and butylenes, are well-known alkylating agents, frequently used in synthesis of alkylated derivatives. Alkylation of benzene is a commercially important process, used to increase the octane rating of fuel and to produce valuable chemical feedstocks. For example, alkylation of benzene with ethylene may be used to produce ethylbenzene, which may be subsequently converted to styrene. Similarly, alkylation of benzene with propylene may be used to produce cumene, which may be subsequently converted to phenol and acetone.
A typical benzene alkylation reaction is shown below:

Older alkylation technology, still widely employed in the petrochemical industry, involves the use of a catalyst based on phosphoric acid. Newer technology utilizes non-polluting, non-corrosive, regenerable materials, such as zeolitic molecular sieve catalysts. U.S. Pat. Nos. 4,371,714 and 4,469,908 disclose straight pass alkylation of aromatic compounds using molecular sieve catalysts in fixed beds. However, there are two main problems arising from the use of zeolitic catalysts in alkylation reactions, namely a more rapid deactivation of the zeolitic catalyst due to cooking and poisoning and a higher yield of polyalkylated by-products.
The first problem often results in frequent unit shut downs or other process interruptions, such as for thermal regeneration of the catalyst. U.S. Pat. No. 5,118,897 further discloses a process for reactivating the zeolitic alkylation catalyst by temporary substitution of the olefin supply stream with a hydrogen stream under certain conditions to shorten the thermal catalyst regeneration cycle.
U.S. Pat. No. 5,856,606 discloses a process for alkylating paraffins including a reaction zone containing a pool of liquid maintained at its boiling point and containing a suspended solid catalyst. U.S. Pat. Nos. 5,019,669, 5,080,871 and 5,118,872 disclose a moving bed reaction system for alkylation of aromatic compounds, in which a slurry is produced by adding solid catalyst to the aromatic feed stream into the reactor. The catalyst slurry circulated through the system may be continuously replaced and regenerated during operation, thus reducing the need for unit shut downs. In some embodiments, these patents also suggest inert distillation packing inside the reactive distillation zone and pressure control to adjust the reactor temperature.
The second problem may be addressed by the use of a second reaction zone for transalkylation of polyalkylate by-products with benzene to increase yield of the desired alkylation product. For example, U.S. Pat. No. 4,083,886 describes a process for transalkylation of alkylate aromatic hydrocarbons that uses a zeolitic catalyst in a fixed bed reactor. U.S. Pat. No. 4,891,458 describes the use of beta zeolite for the alkylation or transalkylation of aromatic hydrocarbons with polyalkylate aromatic hydrocarbons. In one embodiment, the process disclosed includes alkylation or transalkylation using a moving bed catalyst with a catalyst regeneration system. In another embodiment, the invention specifies a jacket or condenser type cooler to maintain constant reactor temperature.
Combining alkylation and transalkylation can thus maximize monoalkylate production. Such a combination can be carried out in a process having two reaction zones, one for alkylation and the other for transalkylation, or in a process having a single reaction zone in which alkylation and transalkylation both occur. For example, U.S. Pat. No. 4,008,290 describes a combination process in which the alkylation effluent and the transalkylation effluent are passed from separate reaction zones to a common separation zone, which separates the two effluents into product, by-product, and recycle streams including a recycle benzene stream.
U.S. Pat. No. 5,003,119 describes a combination process for producing monoalkylate aromatics in which the alkylation effluent passes to the transalkylation reaction zone, and the transalkylation effluent passes to a separation zone. In one embodiment, alkylation and transalkylation reactions take place in different reactors. In another embodiment, alkylation and transalkylation reactions takes place either adiabatically or using interstage cooling.
U.S. Pat. No. 5,902,917 describes a process for producing monoalkylate aromatics, wherein a feedstock is instead first fed to a transalkylation zone and the entire effluent from the transalkylation zone is then cascaded directly into an alkylation zone along with an olefin alkylating agent.
U.S. Pat. No. 5,998,684 describes a process for producing alkylate aromatics that operates with an alkylation zone and a transalkylation zone, where the transalkylation zone and the alkylation zone are arranged for series flow and the transalkylation zone effluent is passed with an aromatic containing feed and the olefinic feed, which is preferably propylene or ethylene, to the alkylation zone. In one embodiment, alkylation and transalkylation take place in separate reactors arranged in series.
Although various processes exist for the alkylation and transalkylation of benzene, as described above, there still exists a need in the art for improved processes for the alkylation and transalkylation of benzene and the removal of benzene from various hydrocarbon feeds.